Help with Redmine (503 error)

I'm trying to get Redmine working with Litespeed, using the instructions on this page:

However, it's giving me a 503 error. I see the following in stderr.log:

2013-04-30 13:15:16.822 [STDERR] /usr/local/lsws/fcgi-bin/RackRunner.rb:13:in `require': no such file to load -- rack (LoadError)
2013-04-30 13:15:16.822 [STDERR] from /usr/local/lsws/fcgi-bin/RackRunner.rb:13

I can confirm that the rack file does not exist in /usr/local/lsws/fcgi-bin/. I also notice that RackRunner.rb is referencing lsapi which does not exist in that directory either.